Four component zoom lens

ABSTRACT

A zoom lens of the type in which a first lens group is divergent and all lens groups are movable and which is suitable for use with still cameras. The zoom lens comprises a first lens group of divergence, a second lens group of convergence, a third lens group of divergence and a fourth lens group of convergence, these lens groups being arranged in the named order in the direction from an object. The second to fourth lens groups are displaceable along a common optical axis in the same direction while they are maintained in predetermined conditions. At the same time, the first lens group is displaceable in the opposite direction so as to contribute to the magnification variance and maintain a predetermined focal point.

sou-mo SR 1 r v \r/ F I- Ullitfid Stat X go a [i Nakamura 1 FOURCOMPONENT ZOOM LENS [75] lnventor: Soichi Nakamura, Kamakura, Japan [73]Assignee: Nippon Kogaku K.K., Tokyo, Japan [22] Filed: Dec. 9, 1971 [21]Appl. No.: 206,359

[30] Foreign Application Priority Data Dec. 15, 1970 Japan 45/111283[52] US. Cl. 350/184, 350/214 [51] Int. Cl. G021) 15/16 [58] Field ofSearch "350/184, 186

[56] References Cited UNITED STATES PATENTS 3,185,029 5/1965 Peck et a1.350/184 2,159,394 5/1939 Mellor et a1. 350/184 3,143,590 8/1964 Higuchi350/184 1 3,771,853 51 Nov. 13,1973

Primary ExaminerJohn K. Corbin Attorney-Joseph M. Fitzpatrick et al.

[57] ABSTRACT A zoom lens of the type in which a first lens group isdivergent and all lens groups are movable and which is suitable for usewith still cameras. The zoom lens comprises a first lens group ofdivergence, a second lens group of convergence, a third lens group ofdivergence and a fourth lens group of convergence, these lens groupsbeing arranged in the named order in the direction from an object Thesecond to fourth lens groups are displaceable along a common opticalaxis in the same direction while they are maintained in predeterminedconditions. At the same time, the first lens group is displaceable inthe opposite direction so as to contribute to the magnification varianceand maintain a predetermined focal point.

9 Claims, 34 Drawing Figures PATENTEDIUV 13 1913 3.771. 853

SHEEY 1 OF 6 f f f 2 3 4 lMAGE s: fszissf 4 l l v i I i I 1 I r I l i II I l I I I I I I SI I $2 I 3 I 84 (f=2e.a5)

P00 x 9500 y PATENTEUNHY 13 mm 3.771. 853 SHEET 2 OF 6 FIG. 2(0) f2 f3f4FIG. 2(b) fl STOP 112 K f3f4 FIG. 2(0) STOP PATENIEDIUY 13 Ian 3.771,853 SHEET 3 or 6 FIG. 3 T

d1 d2 d 5 d4 d 5 PATENTED 1 3 I975 3771.853 SHEET u CF 6 FIG. 6(0) FIG.6(b) FIG. 6(C) -d.5 0 Es FIG.7

0) FlG.7(b) FIG. 7(0) 0 I Z;2s

FIG.8(G) FIG. 8(b) FIG. 8(C) FOUR COMPONENT ZOOM LENS BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a zoomlens in which a first lens group is divergent and all lens groups aremovable.

2. Description of the Prior Art As is obvious from a series ofinverted-telephoto type wide-angle lenses, a lens system having adivergent lens group as a first lens group is convenient for use in alens covering a wide angle of view inasmuch as peripheral beams of lightcan be satisfactorily covered without increasing the diameter of theforemost lens. Such lens system, however, has rarely been adopted foruse in zoom lenses because of the difficulties encountered in correctingthe aberrations caused by the divergent lens group as the first lensgroup. The simplest type of the zoom lenses whose first lens group is adivergent lens group would comprise two lens groups, divergent andconvergent. Such zoom lenses will have disadvantages that the divergentgroup forming the first lens group presupposes a large aperture ratio ofa second lens group which is a convergent lens group, that the sinecondition is extremely variable from negative to positive at theopposite ends of the focal length to thereby seriously aggravate thecoma at those opposite ends, and that the distortional aberrations atthe opposite ends are greatly reversible from negative to positive.These disadvantages would seriously reduce the performance of the zoomlens, and thus the described type of zoom lens may be said to be verymuch inferior in performance to lenses of fixed focal length. This isthe reason why there is practically no zoom lens which has realized theabove-described construction. Also, it has been regarded astheoretically impossible to realize a zoom lens for still cameras ofhigh performances including a wide angle of view, by using theconventional magnification varying system.

SUMMARY OF THE PRESENT INVENTION The present invention intends toprovide an optical system for zoom lenses which has not only solved theforegoing various disadvantages but also can cover a very wide angle ofview such as 74 for a minimum focal distance.

The present invention comprises four lens groups sequentially arrangedin the direction from an object, namely, a first lens group ofdivergence, a second lens group of convergence, a third lens group ofdivergence and a fourth lens group of convergence. The last three lensgroups, i.e., the second lens group of convergence, the third lens groupof divergence and the fourth lens group of convergence are displacedalong a common optical axis in the same direction while maintained inpredetermined conditions which will be described hereinafter, and at thesame time the first lens group of divergence is displaced in thedirection opposite to the direction of movement of the said second tofourth lens groups so as to contribute to the magnification variance andmaintain a predetermined focal point.

The invention will become fully apparent from the following detaileddescription thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 diagrammatically illustratesthe basic construction of the present invention and the process of lensgroup displacement;

FIGS. 2(a), 2(b) and 2(c) illustrate the basic optical path in theconstruction of FIG. 1, showing various lens groups as displaced totheir respective predetermined positions;

FIG. 3 is a longitudinal sectional view of a first embodiment of thepresent invention;

FIGS. 4 and 5 are views similar to FIG. 3, but showing a second and athird embodiment of the present invention;

FIGS. 6(a), 6(b) and 6(0) illustrate the curves representing thespherical aberrations and sine conditions in the first embodiment;

FIGS. 7(a), 7(b) and 7(c) illustrate the curves representing theastigmatisms in the first embodiment;

FIGS. 8(a), 8(b) and 8(0) illustrate the curves representing thedistortional aberrations in the first embodimerit;

FIGS. 9(a) to 11(c) are graphs similar to FIGS. 6(a) to 8(a),respectively, but relating to the second embodiment; and

FIGS. 12(0) to 14(c) are graphs similar to FIGS. 6(a) to 8(0),respectively, but relating to the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will nowbe considered with respect to the construction and arrangement ofvarious elements in the Gaussian range and their process ofdisplacement.

In FIG. I, it is assumed that a first lens group of divergence, a secondlens group of convergence, a third lens group of divergence and a fourthlens group of convergence have focal lengths f,, f f and f respectively,that the inter-principal-plane spacings between the first and secondlens groups, between the second and third lens groups, and between thethird and fourth lens groups are S S and S respectively, and that thespacing between the principal plane of the fourth lens group and theimage plan is 8,. The various elements are determined so as to satisfythe following various conditrons.

n-lsI-s 2 0 fisr- (8mm (Sen) lfsl f2 lfal where ll] (x) and it (x) arefunctions which increase with any variation of x. In contrast, let theamount of displacement of the first lens group be y, which is determinedso as to satisfy the following condition:

4 4 Also, let the combined focal length of the allower lens system be F,which is determined so as to satisfy the following relation:

lull-lawsuit FIGS. 2a, 2b and show the optical path in an example of theoptical system according to the present invention. In these figures ff,, f, and f represent focal lengths of the first lens group ofdivergence, the second lens group of convergence and the third lensgroup of divergence, and the fourth lens group of convergencerespectively. FIGS. 2(a), 2(b) and 2(c) show the positions of the lensgroups for minimum, medium and maximum focal lengths, respectively.

Description will now be made of the formulae determining elements at theminimum focal length side and of the formulae representing the processof lens group displacement.

Formula (1) expresses the basic construction of the zoom lens embodyingthe present invention.

Formula (2) is the condition required at least to provide a sufficientback focal distance of such zoom lens at the minimum focal length side.In view of the application of the present invention to single lensreflex cameras, the back focal distance must be sufficiently long. Inaccordance with formula (2), the zoom lens of the present invention atits minimum focal length side assumes a power arrangement similar tothat of the inverted telephoto wide-angle lens, see FIG. 2(a).Therefore, the value of S must be greater than the sum of the minimumback focal distance of the optical system desired and the spacing fromthe principal point of the fourth lens group to the last vertex of thesame lens group.

Formula (3) is the condition required for the second to fourth lensgroups to assume a triplet type power ar rangement for stableaberrations. This condition is the result of the fact that the absolutevalues of the object point and image point relative to the third lensgroup are greater than f Formula (4) represents the condition underwhich the coma can more readily be corrected if the value of S is assmall as possible at the minimum focal length side which provides aninverted-telephoto type system. More specifically, if the value of S, iswithin that range, the coma at the minimum focal length side can be wellcorrected whereby the balance of such coma with respect to the varyingcoma at the longer focal length side can be well maintained.

Formula (6) means the condition that the distance between the principalplane of the second lens group and a conjugate relative to the imagepoint with respect to composite lens groups of fourth, third and secondlens groups be longer than the focal length f, of the second lens groupin order to increase the power of the first lens group and to determinethe shortest possible spacings between the first lens group and thesecond, third, and fourth lens groups as well as to increase the strokesof the first and second lens groups to thereby provide a greater zoomratio. If this condition is satisfied, a greater zoom ratio may beprovided by a compact construction.

Furthermore, formula (6) combined with formula (5) gives the conditionnecessary and sufficient to provide a positive combined focal length ofthe second to fourth lens groups. This combination is intended to avoidthe inability of the zoom lens system to form a real image when thecomposite lens system provided by the second to fourth lens groupsbecomes a divergent system as a result of the divergence of the firstlens group.

Formula (7) represents the condition required to avoid a complicatedconstruction in which the principal planes of the second and third lensgroups protrude beyond the lens groups due to the positiveinterprincipal-plane spacing between the second and the third lensgroup. Desirably, the second inter-principalplane spacing S, should begreater than the sum of the spacing between the principal point of thesecond lens group and the vertex of the rearmost surface of the secondlens group and the spacing between the principal point of the third lensgroup and the vertex of the foremost surface of the third lens group.

Formula (8) is the condition for making the zoom lens compact inconstruction. According to the conditions of formulae (1) to (6), thecombination of the focal length f, of the second lens group and thesecond inter-principaI-plane spacing S may be of any desired value.However, if the values off and S, satisfying the formula (6) are toolarge, it would enlarge the overall 5 lens system and make it unsuitablefor practical use. This can be avoided by satisfying the condition offormula (8).

Formula (9) is directed to determine the relation I f l S between thefocal Iengthf, of the first lens group 10 and the firstinter-principal-plane spacing S in accordance with the various elementsdetermined by formula (I) to (8), i.e., the fourth inter-principal-planespacing S the third one S,, the second one 5,, the focal length f of thefourth lens group, the focal length f of the of S will increase thespacing between the first and secend lens groups, resulting in anincreased stroke of each lens group and, accordingly, an increased rateof magnification variance.

Formula (10) sets forth the condition for determining the amounts ofdisplacement of the second to fourth lens groups, and this is the basiccondition for the zoom lens system of the present invention. If theamount of displacement (x) of the second lens group is smaller than xwhich is the amount of displacement of the third lens group, then therewill be a great variation in the distortional aberrations at theopposite focal points in the zoom range, which is the problem of firstimportance in a wide angle lens system. For this reason, this formulaspecifies the condition that (x) x.

Also, if the amount of displacement d: (x) of the fourth lens group isequal to or greater than the amountof displacement x of the third lensgroup, there will arise dis- Gaussian range at the minimum focal lengthside is determined so as to satisfy the conditions of formulae (I to (9)and the amounts of displacement of the second to fourth lens groups aredetermined so as to satisfy the condition of formula 10), then theamount of the dis placement of the first lens group required to providea zoom lens will primarily be determined by the formula (I I Thecombined focal length of the overall lens system is given by formula(I2).

Thus, in a zoom lens covering a wide angle of view, the powerarrangement first plays a very important role and then a greaterthickness of each lens group is useful to provide various changes oflens shape.

A zoom lens system which satisfied all of these conditions leads to theprovision of a zoom lens whose lens system is compact but can cover avery wide angle of view and in which each divergent lens group havingfinely corrected distortional and other aberrations also serves as thepreceding image forming system. Such zoom lens is expected to find itsnovel use for still cameras and will develop new camera techniques.

Some embodiments of the present invention will be exemplified hereunder.In all the embodiments which will appear herein, a]; (x) and (x) aregiven as the linear functions of x to simplify the manufacture.Embodiment I This embodiment satisfies the following relations:

(x) 0.8335x A stop is interposed between the third and the fourth lensgroup. The fourth lens group is a doublet which only comprises twoconcave and convex lenses cemented together, as shown in FIG. 3. For theaperture ratio F/4.5 and the focal length F2885 44.19mm, the variouselements of the 35mm still camera zoom lens are selected as follows:

advantages similar to those which have been noted above with respect tothe well-known zoom lens system, simply comprising two divergent andconvergent lens groups. That is, the balance of the sine conditions atthe opposite focal points of the zoom range will be lost, therebyrendering the comas at such opposite focal points difficult to correct.This is the reason why the condition x (x) has been given.

Formula (I 1) relates to the amount of displacement of the first lensgroup. If the power ai-rangement of the Back focus (Bf) 38.299 48.467

In the table above and the tables appearing later, r represents theradius of curvature of each lens, d represents the center thickness andair gap of the lens, n represents the refractive index of the lens glassfor dray, and v represents the Abbe number of the lens glass.

The spherical aberration and sine condition in this embodiment areillustrated in FIGS. 6(a), 6(b) and 6(a), and the astigmatism and thedistortional aberration are illustrated in FIGS. 7(a) 7(b), 7(c) andFIGS,

8(0), (8b) and 8(c), respectively. In each of these figures, (a), (b)and show the aberrations at the minimum, medium and maximum focalpoints, respectively. As will be seen, various aberrations have beenwell corand the astigmatism and distortional aberration are shown inFIGS. 10(a), 10(b), 10(0) and ll(a), ll(b), and (0), respectively. Inthese Figures, (a), (b) and (0) show the aberrations at the minimum,medium and rected and especially correction of distortionalaberramaximum focal points, respectively. It is seen that the tions isas good as in the lenses of fixed focal length. various aberrations havebeen very well corrected and Embodiment ll especially the correction ofdistortional aberrations is Again the same relations as those for theprevious again as good as in the lenses of fixed focal length.embodiment are employed: Embodiment lll MI) L028 In this embodiment, thefollowing relations are satis- (x) 0.8335x fled As shown in FIG. 4,however, a stop is interposed be- M x tween the second and the thirdlens group and the M 0 7836x fourth lens group comprises a doubletsimilar to that of x the fourth lens group in Embodiment l and an addi-The present embodiment attains the extreme position tional convexmeniscus lens attached thereto, to degiven by formula (6). By satisfyingthe relation that crease the distortional aberration. For the aperture111(x) x, the cams for causing displacement of the lens ratio F/4.5 andthe focal length f=28.85 44.19mm, group are simplified and the entiremechanism is also the various elements of the 35 mm still camera zoomsimplified. FIG. 5 shows the zoom lens according to lens are selected asfollows: such embodiment, and the elements of the mm still d1=2.0 n=1.5750l -1=41.3 n=+2sis1 dz=10.5 rl=-5o.121... =-144.se2

d,=4.2 m=LSO6 -2=40.s n=-7a.09i

d.=1.a na=1.44628 3=67.2 r.=+20.967

d =3O.9389-7.7949 ls=+37.907

da=4.5 m=1.60562 u4=43.9 r1=30.741

d1=l.1 r1;=1.744 5=44.9 f|=24.689 =-79.559

d|=3.0 m=1.56883 v6=56.0 'io=+63-793 d1n=4.74105.0912 ru=106.506

du=1.7 n1=1.69895 v7=30.0 f =18-637. m=i0.666

dn=1.0 m=1.79504 ys=2s.4 m=+19.095

d =1.8433-3.8745 ru=+1439.074

d=0.9 m=1.72825 v9=28.3 n5=+20.015

d15=2.6 nm=1.3333 v10=36.8 i4=25.234 1' s=-51.269

du=1.0 n1= -55.0

' d|1=2.3 n11=1.76684 v1l=46.6 m=24.699

Back focus (Bf) 37.728 47.897

camera zoom lens are selected as follows for the aper The sphericalaberration and sine condition in this ture ratio F/4.5 and the focallength f 28.85

Back focus (Bf) 37.768 48.895

The spherical aberration and sine condition in this embodiment are shownin FIGS. 12(a), 12(b) and 12(c). The astigmatism and the distortionalaberration are shown in FIGS. 13(4), 13(b), 13(c) and 14(a), 14(b) and14(0), respectively. In these figures, (a), (b) and show the aberrationsat the minimum, medium and maximum focal points, respectively. It willbe seen that very good correction of various aberrations have been againattained and especially the correction of the distortional aberrationsis as good as in the lenses of fixed focal length.

I claim:

A zoom lens of the type in which a first lens group is divergent and alllens groups are movable, comprising a first lens group of divergence, asecond lens group of convergence, a third lens group of divergence and afourth lens group of convergence, said lens groups being disposed awayfrom an object in the named order and having focal lengths of f,, f,, fand f respectively, said first to third lens groups havinginter-principalplane spacings S S, and S, at their respective minimumfocal length sides, said fourth lens group having a spacing S betweenits principal plane and the image plane, wherein elements of the zoomlens are determined so as to satisfy the following conditions:

whereby the positions of the principal planes of said respective lensgroups at their minimum focal length sides are determined in accordancewith said determined inter-principal-plane spacings, said second, thirdand fourth lens groups being respectively displaced by amounts \Mx), xand 4 (x) from said positions thereof toward the object while satisfyingthe condition:

)z iTEF \p(x) and (pix) are functions increasing" with any variation ofx,

said first lens group being displaced by an amount y while satisfyingthe condition:

Back focus (Bf) 38.299 48.467; wherein: r represents the radius ofcurvature of each lens, d represents the center thickness and air gapbetween lens surfaces, It represents the refractive index of lens glassfor d-ray, and y represents the Abbe number of lens glass.

3. A zoom lens according to claim 1, wherein a stop is interposedbetween the second and third lens groups,

the fourth lens group is a doublet comprising two concave and convexlenses cemented together, and an additional convex meniscus lens, andthe lens satisfies the following conditions:

represents the radius of curvature of each lens, d represents the centerthickness and air gap between lens surfaces, n represents the refractiveindex of lens glass for d-ray and v represents the Abbe number of lensglass.

4. A zoom lens according to claim 1, which satisfies the followingconditions:

where 44(x), x and (x) represent the amounts of displacement of thesecond, third and fourth lens groups, respectively, and \la(x) and (x)are functions which increase with any variation of x; and further thefirst lens groups is displaceable toward an image, while satisfying thefollowing condition:

Back focus (Bf) 37.768 48.895; wherein r represents the radius ofcurvature of each lens, d represents the center thickness and air gapbetween lens surfaces, n represents the refractive index of lens ford-ray and v represents the Abbe number of lens glass.

5. A variable focal length objective lens system consisting in seriation of a first lens group of divergence, a second lens group ofconvergence, a third lens group of divergence and a fourth lens group ofconvergence, all of said groups being movable for zooming,

said second, third and fourth lens groups being displacable toward anobject, satisfying the following condition:

where y represents the amount of displacement of the first lens groups;

13 14 S to 8; represent inter-principal-plane spacings bedoublet ofwhich the cemented surface is concave tween the first and second lensgroups, between the toward the object, and the fourth lens groupincluding second and third lens groups, and between the at least abiconvex doublet of which the cemented surthird and fourth lens groups,respectively; and face is convex toward the object. S, represents thespacing between the principal plane 7. A variable focal length objectivelens system aeof the fourth lens group and the image plane. cording toclaim 6, wherein the second, third and 6. A variable focal lengthobjective lens system acfourth lens groups move by differentdisplacement cording to claim 5, wherein the first lens group includesamount respectively to each other. a negative meniscus single lenselement convex toward 8. A variable focal length objective lens systemacthe object and a biconcave doublet of which the cecording to claim 6,the third lens group moves in unison mented surface is concave towardthe object, the secwith the Second lens group. ond lens group includinga biconvex doublet of which 9. A variable focal length objective lenssystem. acthe cemented surface is concave toward the object and co dingto claim 6, wherein the fourth lens group fura iti e m i i l l l tconvex toward ther includes a positive meniscus concave toward the theobject, the third lens group including a biconcave j UNITEDSTATES-PATENTOFF ICE a v CERTIFICATE OF CORRECTION 7 it Patent No. 1 853Q I I Dated November 13 1973 inventofls) SOICHI NAKAMURA It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown'below:

Column 3, line 47, change "'allower" to alloirer Column 8, in the Table,ch'ange "r =+"889.704" to Column 13, line l-, before"S to S insert for aminimum focal distance of the system Column 13, line 51 "S insert forsaid minimum focaldistance Signed and sealed this 17th day of September197h.

(SEAL) Attest:

MCCOY M. GIBSON, JR. Attesting Officer C. MARSHALL'DANN Commissioner ofPatents USCOMM-DC 60376-P69 F ORM P04 050 (10459)

1. A zoom lens of the type in which a first lens group is divergent andall lens groups are movable, comprising a first lens group ofdivergence, a second lens group of convergence, a third lens group ofdivergence and a fourth lens group of convergence, said lens groupsbeing disposed away from an object in the named order and having focallengths of f1, f2, f3 and f4, respectively, said first to third lensgroups having interprincipal-plane spacings S1, S2 and S3 at theirrespective minimum focal length sides, said fourth lens group having aspacing S4 between its principal plane and the image plane, whereinelements of the zoom lens are determined so as to satisfy the followingconditions: S4 > f4 S3 + f3 <f4S4/S4 - f4 f3 > S3 > 0 f4 - f3 - S3 > OR= 0
 2. A zoom lens according to claim 1, wherein a stop is interposedbetween the third and fourth lens groups, the fourth lens group being adoublet comprising two concave and convex lenses cemented together, andthe lens satisfies the following conditions:
 3. A zoom lens according toclaim 1, wherein a stop is interposed between the second and third lensgroups, the fourth lens group is a doublet comprisiNg two concave andconvex lenses cemented together, and an additional convex meniscus lens,and the lens satisfies the following conditions:
 4. A zoom lensaccording to claim 1, which satisfies the following conditions:
 5. Avariable focal length objective lens system consisting in seriation of afirst lens group of divergence, a second lens group of convergence, athird lens group of divergence and a fourth lens group of convergence,all of said groups being movable for zooming, said second, third andfourth lens groups being displacable toward an object, satisfying thefollowing condition: psi (x) > or = x > phi (x) where psi (x), x and phi(x) represent the amounts of displacement of the second, third andfourth lens groups, respectively, and psi (x) and phi (x) are functionswhich increase with any variation of x; and further the first lensgroups is displaceable toward an image, while satisfying the followingcondition: y S1 + f1 - psi (x) - P where y represents the amount ofdisplacement of the first lens groups;
 6. A variable focal lengthobjective lens system according to claim 5, wherein the first lens groupincludes a negative meniscus single lens element convex toward theobject and a biconcave doublet of which the cemented surface is concavetoward the object, the second lens group including a biconvex doublet ofwhich the cemented surface is concave toward the object and a positivemeniscus single lens element convex toward the object, the third lensgroup including a biconcave doublet of which the cemented surface isconcave toward the object, and the fourth lens group including at leasta biconvex doublet of which the cemented surface is convex toward theobject.
 7. A variable focal length objective lens system according toclaim 6, wherein the second, third and fourth lens groups move bydifferent displacement amount respectively to each other.
 8. A variablefocal length objective lens system according to claim 6, the third lensgroup moves in unison with the second lens group.
 9. A variable focallength objective lens system according to claim 6, wherein the fourthlens group further includes a positive meniscus concave toward theobject.